This invention relates to electronically controlled solenoids and more particularly to a method of determining magnetic characteristics of a solenoid in its finished product state.
A conventional electromagnetic actuator for opening and closing a valve of an internal combustion engine generally includes a solenoid which, when energized, produces an electromagnetic force on an armature. The armature is biased by a return spring and the armature is coupled with a cylinder valve of the engine. The armature is held by the electromagnet in one operating position against a stator core of the actuator and, by deenergizing the electromagnet, the armature may move towards and into another operating position by the return spring.
Conventional high speed electronic solenoids of the fuel injector type include an armature to control movement of an injector valve.
In solenoids of either an electromagnetic actuator or a fuel injector type, it may be desirable, for control or other purposes, to know certain magnetic characteristics of the solenoid. For example, it may be desirable to know when the magnetic circuit approaches saturation, what current levels are expected in order to deliver a desired flux, where significant non-linearities arise along a magnetization curve, how the magnetization curve varies over the operation, life or temperature of the solenoid, or how the current varies due to demands of building flux.
A magnetization curve of a solenoid generally comprises two parameters: magnetic flux density and magnetomotive force. The magnetomotive force is that which tends to produce a magnetic field. In a solenoid, this force is most commonly produced by a current flowing through a coil of wire and the magnitude of the force is proportional to the current and the number of turns of the coil. For simplicity, flux and current may be the two parameters of a magnetization curve.
Since the purpose of a solenoid is to produce a force to perform work and force is the result of a magnetic field (flux), and the magnetic field is the result of electrical current applied to the solenoid, it would seem reasonable that if the current applied was known, the force the solenoid is producing would be known. However, the force the solenoid is producing cannot be obtained by simply measuring current. Due to the variations of magnetic characteristics of the ferromagnetic circuit, the amount of flux and therefore force generated for a given amount of current varies.
Conventionally, the magnetization curve has been assumed, within an error, based on data provided from the manufacturer of the raw magnetic alloy used in the magnetic circuit. Thus, the magnetization curve has classically remained an engineering design variable.
Accordingly, there is a need to determine magnetic characteristics of a solenoid electronically and develop a magnetization curve in a simple and real time output, and to use the magnetization curve in the electronic control of a solenoid.
An object of the present invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is obtained by providing a method of determining magnetic characteristics of an electrically controlled solenoid. The method includes providing an electronically controlled solenoid having an armature, a stator and a coil operatively associated with the stator. The armature, stator and coil define a magnetic circuit. The armature is spaced from the stator to define an air gap between the armature and the stator. Current to the coil is ramped in a generally linear manner over a period of time to define a known current curve. A resulting rate of change of flux in the magnetic circuit is observed and recorded at certain points along the current curve.
In accordance with another aspect of the invention, flux in the magnetic circuit is ramped in a generally linear manner over a period of time to define a known flux curve. A resulting current in the coil is observed and recorded at certain points along the flux curve.
With the above method, a magnetization curve may be developed wherein flux may be determined at any point along a curve for a given amount of current in a solenoid.
Other objects, features and characteristic of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.